Chromic-acid regeneration



R. H. McKEE.

CHROMIG ACID REGENERATION. APPLICATION n'usn SEPT. 4, 1919.

1 ,408,6 1 8 Patented Mar. 7 1922.

UNITED STATES PATENT OFFICE. I

RALPH H. McKEE, OF NEW YORK, N. Y.

CHROMIG-ACID REGENERATION.

Specification of Letters Patent.

Patented Mar. 7, 1922.

Application filed September 4, 1919. Serial No. 321,609.

To all whom it may concern:

Be it known that I, RALPH H. MCKEE, a

a citizen of the United States, residin at New ork andfuric acid which constitutes the principal byproduct of such operations is usually, .in'

practice, permitted to run to waste. Its recovery by chemical processes has-not proven practicable, and although its electrolytic regeneration has many times been proposed, it is not, so far as I amaware, commercially practiced, except occasionally as a discontinuous process.

I have found as the result of many experiments and trials, that chromium sulfate in aqueous solution may be economically transformed into chromic acid by a. continuous electrolytic process in which approximately 80% of the chromium sulfate content of a waste liquor is' reconverted into chromic acid, the resulting regenerated solution, in which the sulfuric acid concentration is substantially the same as in the original sodium bichromate-sulfuric acid mixture, being available for re-use in the oxidation process,

for example the manufacture of camphor,

or anic acids, etc. I

t is a distinctive advantage of my process that it does not involve the neutrallzation and consequent loss of the sulfuric acid content of the waste liquors.

A preferred type of apparatus for use in carrying my process into effect is illustrated in the accompanying-drawing, wherein the figure is a plan view of an electrolytic cell designed for continuous flow. In this figure 10 represents the electrolytic cell, and 11 a porous cup or compartment, which functions as an electrolytic diaphragm, and is best made from a porous silicious material such as that known to the trade as electro-filtros. 12 is the cathode, preferably a sheet of lead, within the porous cup 11: the anodes 13, 13 are also of lead, and are disposed outside of and parallel to the porous cup, the effective anode area being preferably much greater than that of the cathode or cathodes. 14 represents an inlet for the raw liquor to be regenerated, and its flow through the cell is as indicated by the arrows, that is to say, past the cathode 12, thence into the anode compartment through pipe 15 (in addition to the outflow through the walls of the cup 11 hereinafter referred to), thence past the anodes 13, 13, and finally out of the electrolytic field through a siphon or other discharge pipe 16- The liquid discharged at 16 should in a. properly conducted operation be regenerated to the extent of about 80% of its original chromicacid content, although as will be readily understood alarger liquid flow may be used, and

' two or more of the regenerative cells may be arranged in series in the line of flow.

In the practice of the process the level of the liquid in the cathode compartment (that is to say, within the porous cup in the type of apparatus chosen for illustration) is maintained somewhat above that in the outer .cell. with the result that there is at all times some outflow of liquid through the cell-walls and toward the active faces of the anodes. This flow is also indicated by arrows in the figure.

It will be understood by those familiar with this art that the primary function of the cell is to oxidize the chromium sulfate to chromium acid; and that this oxidation takes place at or near the active anode faces: at the same time the concentration of sulfuric acid tends to increase in the region of the anodes and to diminish in the region of the cathode. It is essential however that a suflicient acid concentration should be at all times maintained at the cathode, since otherwise a deposition of chromic hydroxid may occur with resulting clogging-of the diaphragm. According to my invention the acid concentration at the cathode is maintained by the direct supply at that point of a sufficient quantity of the raw liquor, which always contains free sulfuric acid.

Since, however, the effective work of the cell is done at the anodes, it is desirable to limit the supply of raw liquor to the cathode compartment to the volume necessary for maintaining the desired acid concentration. Hence I prefer to provide a supplemental inlet for raw liquor, supplying the same di-' rectly to the anode compartment. In the drawing, this inlet is shown at 17, the arrows indicating the manner in which the stream joins the flow through the anode compartment.

It should be understood however that this is not essential to the practice of the invention, since a practical regeneration may be secured when the entire volume of raw liquor is caused to flow through the cathode compartment I prefer however to supply about two-thirds of the liquor directly to the anode compartment, the remaining one-third sufficing to maintain the proper acid concentration at the cathode.

While the invention is not limited to specific operating conditions, the following are representative of good practice: Current 1.01.2 amp. per sq. dm. anode surface; 3.0-4.0 amp. per sq. dm. cathode surface. Voltage 3.54.0. Acid concentration, anode, 400-600 gm. per liter. Acid concentration, cathode, above 150 gm. per liter.

I claim:

1. A continuous process of oxidizing solu tions containing a salt of chromium, comprising establishing a definite flow of such solution past opposed anode and cathode surfaces separated. by a porous diaphragm,

and passing an electric current between the electrodes.

2. Process according to claim 1, wherein the active anode surface substantially exceeds that of the cathode.

3. Process according to claim 1, wherein the solution flows in opposite directions past the respective electrodes.

4. Process according to claim 1, wherein the liquid volume flowing past the anode is in excess of that flowing past the cathode.

In testimony whereof, I afiix my signature.

RALPH H. MoKEE. 

